Wave-guide antenna



Sept. 29, 1959 G. .1. BROWN WAVE-GUIDE ANTENNA Filed OGC. 19, 1956 R.N mw Nm MB wlw D W M www E G w W H/ la\l H\ E m F ATTORNEYS United States Patent O WAVE-GUIDE ANTENNA Gerald J. Brown, Walpole, Mass., assigner to The Gabriel Company, Cleveland, Ohio, a corporation of Ohio Application October 19, 1956, Serial No. 617,048

11 Claims. (Cl. 343-781) transmission line, for example, has been mounted through the vertex region of a paraboloidal reflector along the vaxis of the reflector, with the mouth of the guide terminating near the reflector focus. A secondary rellector surface positioned beyond. the mouth of the guide'redirects the waves propagated along theguide back upon the paraboloidal reflector, whence the waves are directed as a beam into space. This same structure has, ofcourse, been used, also, as a device for receiving radio waves from space. In order to eect this radio-wave feedingand-directing process eticiently, it has been proposed to terminate the wave-guide mouth, which may be of rectangular cross section, in a resonant chamber of transverse ydimensions larger than the smaller wave-guide 2,907,033 Patented Sept. 29, 1959 ice electric vector. A substantially planar conducting surface closes off the mouth of the guide and extends outward beyond the said side-wall portions of the guide in a plane substantially parallel to the plane of the said electric vector and perpendicular to the longitudinal axis of the wave guide. This antenna has been found to operate very successfully in practice.

There are occasions, however, where strict limitations are placed upon the allowable magnitude of radiation- .side lobes. In addition, increased efficiency is sometimes demanded, namely, greater gain for the same radiation beam width. An object of the present invention, accordingly, is to provide a new and improved slotted Wave-guide structure of the above-described type that provides greatly reduced side-lobe radiation and increased eiliciency. In summary, this end is achieved through providing appropriate conductive chambers overlapping the before-mentioned radiating slots.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawing, Fig. 1 of which is a fragmentary perspective view of the invention in preferred form, partly broken away to illustrate details of construction; and

Fig. 2 is a section upon a larger scale taken upon the line 2 2 of Fig. 1, looking in the direction of the arrows.

AV longitudinally extending wave-guide transmissionline section 1 of rectangular configuration is shown passing through a rectangular hole 2 in the vertex region of transverse dimension. Slots are provided in the surface of the resonant chamber facing the paraboloidal reilector parallel to each of the wider sides of the guide, thereby permitting energy to flow from the slots to the portions of the reector disposed on each side of the guide, or to permit energy to pass from each portion of theretlector into the corresponding slot of the resonantA chamber.

g guide structures, and it is expensive and complicated to manufacture and assemble the associated resonant cham# bers. A further disadvantage of such systems resides in the relatively narrow band of radio frequencies that can be used with tapered guides and resonant chambers.

In copending application of Lan I. Chu, Serial No.

332,839, iiled January 23, 1953, now United States Letters Patent 2,778,015, issued January 15, 1957, for Wave- Guide Antenna, there is disclosed a new and improved antenna embodying a wave-guide transmission line of this character that is not subject to the above-mentioned disadvantagesand that, on the contrary, is easy and lessi" costly to manufacture, and is adapted for wide-band frequency operation. To achieve these ends, the antenna comprises a longitudinally extending wave guide within the interior of which radio waves of predetermined electric-vector polarization may be longitudinally propagated andprovided near its mouth with a pair of slots communicating with the interior of the guide through oppositely disposed transverse side-wall portions of the guide substantially perpendicular to the plane of `the `said-` Vposed preferably at right angles to the guide 1.

a paraboloidal reilector 3 and extending along the axis ofthe 'rellecton The guide 1 is mounted in the vertex region 2 by bolting a bracket 4 secured thereto to the guide section 9 may be connected to a receiver ortrans- .mitten not shown.

The mouth or right-hand end 6 of the guide 1V is'received in a rectangular recess 17 formed intermediately of a circular planar conducting surface or plate 15 dis- The base or end 18 of the recess 17 thus closes olf the mouth 6 of the guide 1. Transverse planar recesses 21, preferably of rectangular shape, are formed, as by milling, in

, oppositely disposed side walls of the wave guide 1, illustrated as the upper and lower walls 16 and 22, near the mouth or end 6 of Vthe guide. Transverse slots 11 are cut,

as explained in the said copending application, through the upper and 'lower walls intermediate the milled re- Ucesses 21 to cooperate with the inner space of the guide y .1, which may be air or any other desired dielectric medivum. In order to protect the slots 11 from the atmosphere and to adapt the medium within the wave guide for pressuring, if desired, windows 19 having substantiallythe same dimensions as the recesses 21 are secured within the recesses 21, thereby hermetically sealing Vthe slots'11.

The thickness of the windows 19'preferably corresponds to the depth of the recesses 21 iny order that the outer facesrof the windows 19 may be substantially ilush with the adjacent outer surfaces of the wave-guide 1. The windows 19 may be of any desired radio-wave transparent material, such as polystyrene and the like, though a preferred window is constituted of Corning type 707 glass. As explained in the said application, the depth of the conducting-surface recess 17 preferably corresponds to,

just slightly less than, the distance D from the mouth 6 of the guide 1 to the edge of each slot 11 further from the reector 3, in order that the said edge may lie sub- Stantally in the plane f the surta@ 0f the smduvting .slate ,1.5, facing the reflector 3 AS Will later be CX- plained, however, certain variations in the position D of the s lot may be tolerated. The ends Vof the milled sections 21 of theguide 1 at the mouth 6 may b e secured'in place in the recess 17 by soft solder, the recess 17 being of somewhat larger dimensions than the transverse guide dimensions in order to permit the securing process to be effected with ease and to :facilitate removal of the same, .if necessary- Ignoring, for the moment, the conducting-chamber surfaces A30 and 32, radio Waves propagated longitudinally along the guide 1 toward its mouth 6, in, for example, the IEol mode, having vertical electric-vector polarization, rrepresented by E, are radiated ltlrlrough the upper and lower slots 11, the slots lying in planes perpendicular t o the electric vector. In the absence of the chambers 30 and 32, the energy radiated 4through the `slots 11 would vbecome initially guided between the upper and lower outer surfaces 16 and 22 of the guide 1 and the adjacent respective upper and lower portions 14 and 20 of the plate 15. From yanother point of view, the slots 11 may be considered as exciting elements disposed substantially along the vertex of a pair of substantially right-angularly disposed corner guiding surfaces 14-16 and 20-22. The energy would thus be directed back along `the upper and lower outer surfaces of the guide 1, reflecting from the upper and lower surface portions 10 and 12 ofthe reilector 3, thereby directed as a beam into space, as explained in the said application. Since the separation between the upper and lower guide side-walls 1 6 and 22 of a rectangular guide operated as above described can be made small compared yto the wavelength of the radio energy, the slots 11 are rather close together and `for all practical purposes behave substantially as a single --point source, thus taking advantage of the parallel-ray focusing properties of the paraboloidal reflector 3 to produce the before-mentioned directive beam in space. The reverse process takes place in reception of energy from space.

The optimum position of the slots 11 for producing the most satisfactory undistorted major radiation lobe in the plane of the electric vector, consistent with maximum antenna gain, has been found to be 4that previously described, with the distance D substantially the same as the depth of the recess 17 so that the slot 11 lies just outside -the plane of the inner surface of the conducting plate 15. It has been determined, however, that satisfactory, though less desirable, results can be obtainedif the slots 11 are disposed somewhat closer to the paraboloidal reflector 3, though intolerable distortion of the radiation lobe patternand loss of antenna gain has been found to occur if the slots 11 are spaced closer to the reector 3 than about one-quarter of the wavelength of the radio energy from the position D Ashown in Fig. l. It Yhas also been determined Ithat the transverse Adimension L of the upper and lower portions 14 and 20 of the plate `15 should have la value of about one-half the said wavelength, though variations `therefrom. up to about three quarters of the wavelength may be tolerated. The length of the slots 11 is rather critical, though variations in the width of the slots maybe eiected. VUndesirable eiects produced by that energy which is reflected from the reflector 3 back in to the 'slots 11 may be minimized with the aid of the previouslydescnibed plate superimposed u pon the rellector 3 about the guide 1. While some energy reilected from the outer portions of the reilector 3 may're-enter the slots 11, cancellation or substantial cancellation thereof at the slots 11 has been found'to occur as a result of reflections `from the surface of plate 5 protruding closer to the -slots -1'1 than the adjacent portions ofthe reflector 3. This eect, moreover, takes place over a relatively broadband of frequencies.

vIn 'accordance with the present invention, however, the slots 11 are not left free to radiate upward and downward into space as in the antenna of ithe said copending .substantially a Yhalf-wavelength from the end plate V1S,

and even up to substantially threefquarters of the wavelength; and, if, secondly, the chamber height is substantially `that of the dimension L of Athe end yplate 15, an extremely beneficial result takes place. That result is the vastly improved reduction in side lobes of the radiation pattern and increased radiating efficiency. The explanation of this experimentally verified result may reside in the fact that the chambers 30 and v32. will be excited by radiation vthrough the slots 11, acting as wave-guide radiators having substantially the same mode of electromagnetic eld as the original guide 1. The radiation that normally spills over or is wasted when the slot radiation upward and downward is uncontined, as in the antenna of the said copending application, contributes to the production of side lobes and the diminution of energy in the primary radiation lobe or pattern. Since this slotvradiated energy is now conned to travel through the chambers 30 and 32 directly frearward toward the reflector 3, in Aaccordance with the present invention, more energy is maintained in the primary lobe, resulting in greater eciency and markedly reduced side-lobe radiation.

I n order to simulate a point source, as before mentioned, -the slots 11 may be brought closer together by reducing the height of the terminal section of the guide 1 containing the slots 11. The point of transition between the Aleft-band greater-dimensional guide section 1 and the said terminal section should `belocated suiciently rearward of the apertures or mouths of the chambers 30 and 32 to prevent restriction of the energy directed therefrom. A guide 1 of uniform dimensions throughout,

however, may be employed, if desired. The apertures or mouths of the chambers 30 and 32 may be covered with weatherproof, radio-wave permeable Windows, `not shown, as of polystyrene and the like.

`While, in some cases, the chambers 30 and v32 might constitute merely walls of a cylinder extending real'- ward from the complete peripheral border of the plate 15, it is often desirable to maintain the horizontal radiation pattern relatively broad. This is achieved by limiting the maximum ltransverse dimension of the chambers -30 and 32 to the width of the `guide 1, as by terminating the surfaces -30 and 32 at the side Walls of the guide 1, -as shown. 'Other surface congurations 30 and 32, including rectangular chambers, may also be employed, though the illustrated oval configuration has been found to operate very satisfactorily.

Not only does the above-described construction eliminate the necessity for tapering the wave guide and for providing resonant slotted chambers, but this construction is admirably vsuitelto rapid and accurate mass-production techniques. I thas been observed that this structure, in

addition, illuminates orffeeds the reflector aperture in such a manner as to provide greatly reduced secondary lobes in the radiation patternand increased eh'iciency.

an illustration of typical dimensions, given in units of inches Vinstead of fractions of a wavelength, though about 52 of an inch-fior optimum results. -F[Ehe-plate 15 may be of circular contour, about 2%6 inches in diameter.

For substantially half-wavelength long chambers -30 and 32 and a six-foot parabolic reflector, moreover, extremely low-energy secondary lobes 29 and 26 decibels down, have been produced in the vertical and horizontal radiation pattern, respectively. The half-power beam widths of the principal vertical and horizontal lobes were 1.8 and 1.6, respectively.

While, as before explained, the rectangular guide 1 is particularly well-suited to the purposes of the present invention inasmuch as the height dimension, shown vertical, may be small compared to the wave length of the radio energy, so that the slots 11 may be close together, if some distortion can be tolerated, the same technique may be applied to Wave guides of other configuration, such as guides that are oval, including substantially circular, in cross section.

While, moreover, the invention has heretofore been described in connection withthe use of such systems as vtransmitting apparatus, it is to be understood that they are equally well suited for the reception of radio waves. The slotted wave guide and end-plate structure, moreover, may find application as an antenna in and of itself, without the use of a surface reector 3, to obtain radiation patterns of the character produced by such a slotted guide. If desired, furthermore, but a single slot may be utilized where symmetrical results are not'wanted. A plurality of unsymmetrically disposed slots may also be employed, if unsymmetrical patterns are to be achieved, the plurality of slots, for example, being parallel to one another on one side only of the guide. While the slots 11 have been shown as provided with rounded ends, this is merely because a milling machine may produce such ends. It is to be understood, however, that the slots may be of strictly rectangular or other configuration and that they may be formed by punching and other processes as well. Similarly the plates 15 may be other configuration than circular. The length and orientation of the slots may also be varied depending upon the desired radiation pattern configuration. As a further illustration, the terminal slots may be provided in the narrower side walls parallel to the wave-guide axis and perpendicular to the end plate 15.

Further modifications will occur to those skilled in the art and all such are considered to fall Within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A longitudinally extending wave guide closed at one end having a slot in a wall of the guide near the said end, a rst conducting surface disposed at an angle to the wave-guide at the said end and extending transversely beyond the said wall, and a second conducting surface extending longitudinally from the first conducting surface back along the said wall overlapping the said slot and terminating along its side edges at the side edges of the said wall of the guide.

2. A longitudinally extending wave guide closed at one end having a slot in a wall of the guide near the said end, a first conducting surface disposed at substantially right angles to the wave guide at the said end and extending transversely beyond the said Wall, and a second conducting surface extending longitudinally from the first conducting surface back along the said wall overlapping the said slot and terminating along its side edges at the side edges of the said wall of the guide.

3. A longitudinally extending wave guide closed at one end having a slot in a Wall of the guide near the said end, a first conducting surface disposed at an angle to the wave guide at the said end and extending transversely beyond the said wall, and a second conducting surface extending longitudinally from the first conducting surface back along the said wall and shaped to provide a chamber having the said wall and the first conducting surface as its other bounding surfaces overlapping the said slot in order to be excited by radiation passing through the slot and terminating along its sideedges at the side edges of the said wall of the guide. Y

4. A longitudinally extending Wave guide closed at one end having a slot in a wall of the guide near the said end, a first conducting surface disposed at an angle to the wave guide at the said end and extending transversely beyond the.said wall, and a second conducting surface extending longitudinally from the first conducting surface back along the said Wall and shaped to provide a chamber having the said wall and the first conducting surface as its other bounding surfaces and overlapping the said slot in order to be excited by radiation passing through the slot, the dimensions of the chamber being sufficient to establish therein substantially the l same wave-guide propagation mode as is established' within the guide.

5. A longitudinally extending wave guide closed at one end having a slot in a wall of the guide near the said end, a first conducting surface disposed at an angle Yto the wave guide at the said end and extending transversely beyond the said wall, and a second conducting surface extending longitudinally from the first conducting surface back along the said wall and shaped to provide a chamber having the said wall and the first conducting surface as its other bounding surfaces and overlapping the said slot in order to be lexcited by radiation passing through the slot, the chamber terminating at the sides of the said wall in order to provide a chamber aperture the width of which corresponds to the width of the guide between the sides of the said Wall. 6. A longitudinally extending wave guide closed at one end having a slot in a wall of the guide near the said end, a first conducting surface disposed at an angle to the wave guide at the said end and extending transversely beyond the said wall, and a second conducting surface extending longitudinally from the first conducting surface back along the said wall and shaped to provide a chamber having the said wall and the first conducting surface as its other bounding surfaces and overlapping the said slot in order to be excited by radiation passing through the slot, the chamber being of oval cross-section and terminating at the sides of the said wall in order to provide a chamber aperture the maximum width of which corresponds to the width of the guide between the sides of the said wall.

7. A longitudinally extending Wave guide closed at one end having a pair of slots in oppositely disposed side walls of the guide near the said end, a rst conducting surface disposed at substantially right angles to the said side walls of the wave guide at the said end and extending transversely beyond the said side walls, and further conducting surfaces extending longitudinally from the first conducting surface back along the said side Walls overlapping the said slots and terminating along their side edges at the side edges of the said walls of the guide.

8. A longitudinally extending wave guide closed at one end having a pair of slots in oppositely disposed side walls of the guide near the said end, a first conducting surface disposed at substantially right angles to the said side walls of the wave guide at the said end and extending transversely beyond the said side walls, and further conducting surfaces extending longitudinally from the rst conducting surface back along the said side Walls shaped to provide chambers overlapping the said slots in order to be excited by radiation passing through the slots and terminating along their side edges at the side edges of the said walls of the guide.

9. A longitudinally extending wave guide closed at one end having a pair of slots in oppositely disposed side walls of the guide near the said end, a first conducting surface disposed at substantially righ-t angles to the said side walls of the wave guide at the said end and extending transversely beyond the said side walls, and further conducting surfaces extending longitudinally from the first conducting surface back along the said side walls and shaped to provide chambers overlapping the said slots in order to be excited by radiation passing through the slots, the chambers terminating at the sides of the said side walls of the guide in order to provide chamber apertures the width of which correspond to the width of the guide. l0. A longitudinally extending wave guide closed at one end having a pair of slots in oppositely disposed side walls or the guide near the said end, a first conducting surface disposed at substantially right angles to the said side walls of the wave guide at the said end and extending transversely beyond the said side Walls, and further conducting surfaces extending longitudinally from the first conducting surface back along the said side walls and shaped to provide chambers overlapping the said slots in order to be excited by radiation passing through the slots, the chambers being of oval cross-section and terminating at the sides of the said side walls of the guide in order to provide chamber apertures the maximum width of each of which corresponds to the width of the guide.

11. A Wave guide as claimed in claim 1 and in which the slot is positioned a distance from the rst conducting surface corresponding to or less than substantially onequarter the wavelength` of the energy to be propagated within the Wave guide, the first conducting surface extends transversely beyond the said Wall of the guide a distance corresponding to from substantially one-half to threequarters of the said Wavelength, and the second conducting surface extends longitudinally a distance corresponding to from substantially one-half to three-quarters of the said wavelength.

References Cited in the le of this patent UNlTED STATES PATENTS 2,566,900 McArthur sept. 4, 1951 2,778,016 Chu Jaa 15, 1957 FOREIGN PATENTS 708,614 Great Britain May s, 1954 

